In conventional oil and gas operations, a well is typically drilled to a desired depth with a drill string, which includes drill pipe and a drilling bottom hole assembly (BHA). Once the desired depth is reached, the drill string is removed from the hole and casing is run into the vacant hole. In some conventional operations, the casing may be installed as part of the drilling process. A technique that involves running casing at the same time the well is being drilled may be referred to as “casing-while-drilling.”
Casing may be defined as pipe or tubular that is placed in a well to prevent the well from caving in, to contain fluids, and to assist with efficient extraction of product. When the casing is properly positioned within a hole or well, the casing is typically cemented in place by pumping cement through the casing and into an annulus formed between the casing and the hole (e.g., a wellbore or parent casing). Once a casing string has been positioned and cemented in place or installed, the process may be repeated via the now installed casing string. For example, the well may be drilled further by passing a drilling BHA through the installed casing string and drilling. Further, additional casing strings may be subsequently passed through the installed casing string (during or after drilling) for installation. Indeed, numerous levels of casing may be employed in a well. For example, once a first string of casing is in place, the well may be drilled further and another string of casing (an inner string of casing) with an outside diameter that is accommodated by the inside diameter of the previously installed casing may be run through the existing casing. Additional strings of casing may be added in this manner such that numerous concentric strings of casing are positioned in the well, and such that each inner string of casing extends deeper than the previously installed casing or parent casing string.
Liner may also be employed in some drilling operations. Liner may be defined as a string of pipe or tubular that is used to case open hole below existing casing. Casing is generally considered to extend all the way back to a wellhead assembly at the surface. In contrast, a liner merely extends a certain distance (e.g., 30 meters) into the previously installed casing or parent casing string. However, a tieback string of casing may be installed that extends from the wellhead downward into engagement with previously installed liner. The liner is typically secured to the parent casing string by a liner hanger that is coupled to the liner and engages with the interior of the upper casing or liner. The liner hanger may include a slip device (e.g., a device with teeth or other gripping features) that engages the interior of the upper casing string to hold the liner in place. It should be noted that, in some operations, a liner may extend from a previously installed liner or parent liner. Again, the distinction between casing and liner is that casing generally extends all the way to the wellhead and liner only extends to a parent casing or liner. Accordingly, the terms “casing” and “liner” may be used interchangeably in the present disclosure. Indeed, liner is essentially made up of similar components (e.g., strings of tubular structures) as casing. Further, as with casing, a liner is typically cemented into the well.
Whether casing or liners are used for any particular well, the casing or liner strings are run into the wellbore using a running tool. In conventional approaches, a mechanically and/or hydraulically actuated casing running tool includes a wedge shaped element that is engaged between the central mandrel of the tool and the inner bore of the casing or liner by means of axial motion. These wedges may self-actuate further due to the weight of the casing string itself, providing a fail-safe mechanism when engaged due to the tool continuing to grip even in the event of power-loss to the engagement mechanism. Such an approach, however, creates issues related to providing sufficient engagement between the running tool and the liner or casing when there is limited weight suspended from the string which, as noted above, is self-energized due to the action of gravity. For example, in current approaches, a hydraulic system separate from the main drive system (i.e., the top drive) may be employed to engage and disengage the running tool and the casing or liner.